GEC Functions/Misfunctions

[grandpapastu]

Walking down the street I notice the 120/240 1-PH overhead service drop to a neighbors residence drooping dangerously low crossing the street to his house. On further observation I discovered that the grounded conductor of the service drop triplex had been severed at the utility pole.

I promptly alarmed the neighbor to the condition, instructed him to disconnect all loads from the service by the outside main disconnect (system uses a 200A MLO loadcenter) and advised him to get the utility provider out on an emergency service call.
Before the system was shut down I noticed lights and ceiling fans operating and he indicated no unusual conditions at all. I did not investigate further. The service drop was repaired. I have not surveyed the system since the repair.
Any experience or thoughts on the function of the GEC system in all of this?

 

[bphgravity]

Re: GEC Functions/Misfunctions

My guess is that the neutral return current was using the grounded service conductor from the house next door through the two systems grounding electrodes. This would be especially true if both are connected to utility water pipes.

 

[charlie tuna]

Re: GEC Functions/Misfunctions

or during this period the load was close to be balanced--- maybe the voltage was 140 on one side and 100 on the other -- the appliances will function!!!

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Good. I am on the same page.
However, just walked down that way to grab a beer from the store and observed that the neighbor's service is on the opposite side of the house from the other.

I believe, though I may be wrong, that the path of least resistance for current flow back to source would be directly across the street via earth to the ground rod driven at the base of the supplying utility pole.
Now here is the tick: a number of utility pole GEC are cut (hand level) to the ground rods at the base of te poles. If that had been the case here and my above noted hypothesis is correct then it would follow ,in that case, that my neighbor would have been putting out quite a few fires from appliances and fixtures and such. What ya think?

 

[grandpapastu]

Re: GEC Functions/Misfunctions

charlie tuna -
Can you elaborate/explain.
I can think it out of course and at the same time want your input.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Any assist please?
Current flows as always back to the source by path of least resistance.
Cut the neutral of any multi circuit junction, whether it is a three circuit junction in a 1900 box or a 42-circuit junction in a loadcenter and current and full difference of potential will be experienced on the load or loads.
Load may be the filament of a light bulb, a toaster oven or a transformer of a stereo receiver.
Balanced loads would result in little to no load on the neutral back to source. Without a neutral back to source then the only other route back to source will have to be the other phase conductor.
240VAC across a 120VAC TV, or VCR, or toaster oven will start a fire.

 

[jim dungar]

Re: GEC Functions/Misfunctions

First: current does not only flow over the path of least resistance. Current flows over all available pathes in an inverse ratio to their resistances.

If you have two resistors in series, the same current will flow through each. The current flow will cause a voltage drop across the resistor directly proportional to it's resistance.

So for two equal (balanced) loads in series connected to 240V, each load "sees" 120V even though there is no neutral connection.

 

[tom baker]

Re: GEC Functions/Misfunctions

GEC and GES will have no effect on an open neutral as the resistance of the earth is too high to clear a fault or serve as a conductor. See 2005 NEC 250.4(B)4, last sentance.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

O.K. bout to walk out for another beer, but, before that:
are you saying that three identical loads such as three identical make and model VCR connected to the same grounded conductor, energized, (a multicircuit) when interupted/severed from it's neutral connection at junction that the loads will not experience overvoltage?
Anyway, all loads in series or parallel juncture at the panel (loadcenter) with current in-route back to source and are not in series with each other but parallel.
Currents from PH-A and Currents from PH-B meet or juncture at the grounded conductor buss at the loadcenter.
Literally:
This is not a series circuit I am discussing.

 

[karl riley]

Re: GEC Functions/Misfunctions

If the services are grounded to metal water pipes, the neutral current will use the pipes to get to a neighbor's neutral and return to the Tfrmr that way, so the voltage will stay more or less normal. This is a dangerous situation since the open neutral has been masked.

When the service neutral is open, PhA loads and PhB loads in the building will be in series, not parallel. If loads are balanced, they will share 240V equally. If they are not balanced the voltage of the hot legs will vary with the impedance of the loads. Burned out appliances and light bulbs.

Lucky you noticed the cut neutral.

Karl

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Good.
Let's look at a series circuit of 240 VAC with 160A continuous current available.
Circuit is wired: three ceiling fans, six incandescent luminairs, one toaster, a TV, and a VCR, recirculating pump for the goldfish, a radio in the back room.
Circuit is wired with 4/0 Al THWN, 12AWG CU NMB, and 14AWG CU NMB.
Add it up and what do you have?

R1+R2+R3+Rn=RT in a series circuit.
I1=I2=I3=In=IT in a series circuit.
OHMS Law:
E/R=I ???
Something like that?

I was not discussing series circuits.
I was discussing overvoltage condition. Each link in the chain is only as strong as the strongest link in the chain.
Am I wrong here? Was I wrong here?
Sure. Ofcourse I was; Overcurrent starts the fire.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Jim Dungar:
Yes Sir.
We are both right.
In the case I outlined the current flow will mostly be on the path of least resistance.
Electric current always and always will seek the path of lease resistance to source.
In parellel circuits this is proven by the fact of more current flow across the paths with less resistance.
I never said that electric current seeks only the path of least resistance back to source.

You are right: even though the neighbor's service is on the opposite side of the house and away from the direction of the source this will be considered a parellel circuit, although of negligable value.
Of course by my explanation you had no way of knowing what the exact values of current flow across each of the two paralel paths back to source could be.

 

[grandpapastu]

Re: GEC Functions/Misfunctions

Jim Dungar:
Yes Sir.
We are both right.
In the case I outlined the current flow will mostly be on the path of least resistance.
Electric current always and always will seek the path of lease resistance to source.
In parellel circuits this is proven by the fact of more current flow across the paths with less resistance.
I never said that electric current seeks only the path of least resistance back to source.

You are right: even though the neighbor's service is on the opposite side of the house and away from the direction of the source this will be considered a parellel circuit, although of negligable value.
Of course by my explanation you had no way of knowing what the exact values of current flow across each of the two paralel paths back to source could be.

 

[charlie tuna]

Re: GEC Functions/Misfunctions

grandee,
from some of your comments--it seems as though you think the ground rods at the pole bases or the ground rings at the pole bases actually have an effect on a return path back to your service. although they do - please be advised they are probibly minute!!! where do you live and under what conditions do you think you have a low resistance path from your ground rod back to your power company's transformer neutral point???

 

[stud696981]

Re: GEC Functions/Misfunctions

Just one comment based on the original poster. If the other house is on the opposite side of the street and both have metalic piping, it's all connected so it doesn't matter if it's next door or down the block. When the whole area has metalic pipes and everyone is bonded to them, a neutral can come open on the service drop and things will still function because the water piping is acting just like the neutral since they are all connected.

 

[mdshunk]

Re: GEC Functions/Misfunctions

Originally posted by grandpapastu:

In the case I outlined the current flow will mostly be on the path of least resistance.
Electric current always and always will seek the path of lease resistance to source.

Nope... Reference Kirchoff's Law. Current will flow on ALL available paths. More current will flow on the least resistive paths, and less current will flow on paths of higher resistance. Still, all paths will be utilized to some extent.

 

[bphgravity]

Re: GEC Functions/Misfunctions

I think the more important question is how much current should be permitted to flow on the grounding electrode system before it becomes objectionable. This is where the code seems to contradict itself. We want all the neutral current to flow on the insulated grounded utility path, yet the code calls for an extensive grounding system which invites neutral current through those paths.

The NFPA 780 indicates two 10' ground rods are sufficient to carry lightning surges to Earth. The total impedance of those rods is ot all that important. Per the requirements of the NEC, a typical structure could achieve a very low resistance Earth path if all "present" electrodes are used. These seems unnecessary and possibly a problem. Stray voltages are becomming an ever increasing problem for utility and power companies.

Earth may indeed be insufficent as an effective fault path, but it most certainly is effective enough to carry currents lethal to humans and animals.

 

[pierre]

Re: GEC Functions/Misfunctions

From Bryan

"Stray voltages are becomming an ever increasing problem for utility and power companies.

Earth may indeed be insufficent as an effective fault path, but it most certainly is effective enough to carry currents lethal to humans and animals."


'The more things stay the same, the more they change.'


Stay the same:
Grounding to cold water

More they change:
Where current paths have changed (stray voltage)

 

[charlie tuna]

Re: GEC Functions/Misfunctions

i think it has become apparent over the last ten to fifteen years that our industry's dependency on the ground rod being a secondary return path to the power source is weakening! some of this, no doubt, is caused by less auxilary system contact with the earth or surface contact--copper or galvanized pipe---water and gas and also more current flow on service neutrals due to more basic electrical load! water and gas service pipes are now plastic --- interior piping is plastic --- there is only a small amount of conductive material for these systems to be in direct contact with the earth!

i can only speak from my past expieriance concerning ground rods being used to limit damage to the system when struck by lightning, and i have seen it come in on the service riser and jump through the attic and down into appliances. wouldn't you think from the service riser it would follow a low impedence path into the ground rod??? i have seen it come in the cable tv service, jump across and onto some home run raceways, then back to the main service panel and back out into circuits damaging appliances throughout the residence. again, if it was in the main panel, wouldn't you think it would dissapate back to and through the electric ground system? again, "modern times" has increased the severity of the damage because years ago we had only a small amount of appliances that were actually enegized, even though they were not in use. today's computerized "everything" gets fried--micro--dishwaher--wash machine--refrig--freezer--computers--toaster oven--coffee pots--etc.. twenty years ago, we didn't realize a strike occured--maybe the kitchen clock stopped working - it might have been the only appliance connected and energized???

whats the answer??? the power companies and ground rod manufacturers ain't gonna like it -- four wire service drops. two insulated hots, one insulated neutral and a bare bond wire and no ground rod! the sooner we all realize the fact that the ground rod does little to reduce the impeadance back to the power source the safer our systems will be! as long as we drive these ground rods -- we are basically "living in a myth"! when you can live in florida and drive a gound rod 60 feet down ---thats 56 feet in contact with water and earth---and your power source is 125 feet away with a standard utility ground array and it woun't clear a 15 amp ground fault---"it ain't a very good system"!!!

 

[pierre]

Re: GEC Functions/Misfunctions

"whats the answer??? the power companies and ground rod manufacturers ain't gonna like it -- four wire service drops. two insulated hots, one insulated neutral and a bare bond wire and no ground rod!"

AMEN!!!

But, this will never happen...not in my life time at least.